Thermoplastic materials useful for producing flexible or rigid articles for food packaging are well known.
Such an article may either retain or repel water vapor from the contents and/or prevent the transmission of oxygen into the contents, respectively. For example, when oxygen penetrates into a article it will combine with oils and cause off-taste and rancidity. Other food products, such as foods having a high starch or sugar content, can be damaged by picking up water.
There has, therefore, been a long felt desire on the part of the food packaging industry to have a relatively inexpensive plastic article which provides excellent oxygen and water vapor barrier properties, and which withstands article failure at different temperatures.
Such articles can typically be formed from single-layered or multi-layered structures. Typically, if the article is formed from a multi-layer structure, it has at least one outside, or skin, layer, a barrier layer, and an adhesive, or tie, layer interposed between each skin layer and the barrier layer. Thus, in a thermoplastic structure having one outer layer and one inner layer, there will be one tie layer therebetween. In a structure having three thermoplastic layers, there will be two tie layers provided. Generally, in multi-layered structures the inner and outer layers are coextruded with the tie layer therebetween.
Such articles are useful for the packaging of dry food stuffs which must be kept in low water content as, for example, dried soup and gravy mixes or powdered sugar; of foods that require that a water content be maintained such as condensed soups, canned fruits and vegetables; or food which must be kept free from oxygen permeation such as meat products or other like foods containing oils or fats.
The price of metal cans over the past years has continued to increase while that of many plastic materials has decreased. In addition to lower cost, other benefits of plastic articles include relatively easy disposal, in that plastic can be burned: cleanliness, in that plastic does not rust; elimination of permanent denting which is common in metal cans: and microwaveability.
It has been found that with a plastic article having walls comprised of different materials that proper choice of layer materials can also render the articles heat retortable for sterilization of the contents after packaging thereof in the articles, thereby giving the packaged food an extended shelf life without requiring refrigeration.
It is an object of the present invention to provide a composition useful as the tie layer for a multilayer structure, which composition has improved adhesion to the skin layer(s) and the barrier layer.
It is a further object of the present invention to provide a multilayer plastic container for the storage of food products which not only has high moisture and gas barrier properties but also has improved peel strength among the layers.